Terminal Velocity
Forces and Motion

Free Fluid

At home for 5-11 11-14


What you need

  • A large plastic bottle
  • Scissors
  • Some water
  • An outdoor space

Instructions

  1. Cut a hole about 1cm across in the side of the bottle and stand it on the ground
  2. Keep your finger over the hole and fill the bottle with water
  3. Take your finger away – water should spurt from the hole
  4. Repeat what you did, but drop the bottle from above shoulder height as you remove your finger. This time, no water pours from the bottle while it falls

Results and Explanation

In the standing bottle, gravity pulls on the water so it presses on the bottom and sides and escapes through the hole. When you drop the bottle, both it and the water fall at the same rate so the water doesn’t press on anything – it’s as if it was floating inside the bottle.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.

Terminal Velocity
can be analysed using the quantity Drag Acceleration
is a special case of Velocity
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